Coherent control of injection currents in high-quality films of Bi2Se3

TL;DR

This study demonstrates coherent control of injection currents in high-quality Bi2Se3 films through quantum interference, confirming third-order nonlinear optical effects and analyzing optical transitions with a tight-binding model.

Contribution

It presents the first demonstration of quantum interference control of photocurrents in high-quality Bi2Se3 films grown by molecular beam epitaxy.

Findings

Injection current depends linearly on fundamental pulse irradiance.

Square-root dependence observed with frequency-doubled pulses.

Injection current exhibits sinusoidal dependence on relative phase.

Abstract

Films of the topological insulator Bi2Se3 are grown by molecular beam epitaxy with in-situ reflection high-energy electron diffraction. The films are shown to be high-quality by X-ray reflectivity and diffraction and atomic-force microscopy. Quantum interference control of photocurrents is observed by excitation with harmonically related pulses and detected by terahertz radiation. The injection current obeys the expected excitation irradiance dependence, showing linear dependence on the fundamental pulse irradiance and square-root irradiance dependence of the frequency-doubled optical pulses. The injection current also follows a sinusoidal relative-phase dependence between the two excitation pulses. These results confirm the third-order nonlinear optical origins of the coherently controlled injection current. Experiments are compared to a tight-binding band structure to illustrate the possible optical transitions that occur in creating the injection current.